There have been numerous attempts in the prior art to provide a transmission of the continuously variable type for automotive use. A continuously variable transmission can substantially boost fuel economy because engine speed can easily be pulled back to the most efficient point for the road condition. Additionally, this type of transmission can be much smoother in operation than a typical stepped type automatic transmission. Some transmissions of the prior art have utilized hydraulic means for power transfer and to effect a change in speed ratio. These transmissions have a long service life but deliver poor efficiency due to fluid turbulence losses. Other transmissions use a belt between V-type pulleys with moveable sheaves to transmit power and effect speed ratio changes. Changing the width of the pulleys changes the diameters of the circles on which the belt runs, thus changing the speed ratio between pulleys. These moveable sheave transmissions are more efficient than the hydraulic transmissions, but have a short service life due to wear of the belts and pulleys. Two types of moveable sheave transmissions have had limited success in automotive use. One type uses a rubberized belt to transmit power between pulleys. This type has a low torque capacity because of the limited pressure that can be applied to the belt material by the pulley sheaves. A second type uses a belt of stacked metal wafers for power transmission. The stacked metal wafers provide a push force between pulleys, rather than the pull force that is characteristic of the rubberized belt design. The higher pressure that can be applied to this metal belt by the pulley sheaves increases the torque capacity somewhat over the rubberized belt type. The torque capacity of is limited however, because of the spacing between wafers that is necessary for the belt to be able to bend radially around the arc of the pulleys. This spacing causes the wafers to cock at an angle relative to the radial lines of the pulley sheaves during the transmission of power. This places the wafer edges over a radius on the pulley sheaves, rather than over the straight surface at the radial lines of the sheaves. This severely decreases the area of contact between the edges of the wafers and the surfaces of the pulley sheaves, and so reduces the torque capacity of the transmission per unit size. The cocking movement of the wafers also causes wear between the edges of the wafers and the pulley sheaves, which shortens the service life of the transmission.
While substantial progress has been made in the prior art in providing a continuously variable transmission that is suitable for use in an automobile, there remains a need for a transmission of high efficiency that has an extended service life and a higher torque capacity relative to size.